The present invention relates to a method and apparatus for classifying white blood cells (leukocytes) and, particularly, to a leukocyte classifying apparatus capable of automatically classifying neutrophils into band form neutrophils and segmented neutrophils accurately.
Blood cells are produced in the marrow, and they have various forms in each phase of growth and ultimately flow in peripheral blood. Blood cells include leukocytes, erythrocytes and thrombocytes. Leukocytes have structural information which indicates the presence or absence of blood diseases such as leukemia and other diseases.
Classification of leukocytes is to classify grown leukocytes or detect and classify immature leukocytes using smeared and stained blood samples. Grown leukocytes fall into neutrophils, eosinophils, basophils, monocytes and lymphocytes. Neutrophils, which amount to about 55% of human peripheral blood, are subdivided into band form neutrophils 11 each having a single nucleus as shown in (a) of FIG. 1 and segmented neutrophils 12 with its nucleus constricted and separated into two or more as shown in (b) of FIG. 1. The ratio of the quantities of the two types of neutrophils is related to the blood diseases, and therefore it is necessary to classify neutrophils accurately.
One method of classifying neutrophils is based on the count of nucleus mask pattern components, N.sub.c, calculated by the nucleus mask pattern extraction method to determine each nucleus to be a band form nucleus when N.sub.c =1, or to be a segmented nucleus when N.sub.c .gtoreq.2. Namely, when a nucleus mask pattern 2 consists of two islands 3 and 4 linked by a broad bridge, as shown in (a) of FIG. 1, the islands 3 and 4 are assumed to constitute in combination one component, and when a nucleus mask pattern 6 consists of two islands 7 and 8 linked by a narrow bridge as shown in (b) of FIG. 2, each of the islands 3 and 4 is assumed to constitute one component. The method of extracting a nucleus mask pattern is disclosed in Japanese Patent Application Laid-open No. 53-13491, and the method of counting components of a nucleus mask pattern is disclosed in Japanese Patent Application Laid-open No. 51-95799.
There has been proposed a modified method in which the above-mentioned classifying method is added by the process for detecting holes in the nucleus mask pattern caused by the improper contrast of the nucleus image and for filling the holes, and the process for separating bridged components of a segmented neutrophil. This method has been realized on an approximation basis through the process of coarse sampling of a nucleus mask pattern, as disclosed in Japanese Patent Application Laid-open No. 53-52495. All of the foregoing methods, however, are apt to determine the number of pattern components to be N.sub.c =1 for the cases of a segmented neutrophil 21 with its islands of nucleus in contact with each other as shown in (a) of FIG. 2, or a segmented neutrophil 22 with its islands of nucleus overlapping as shown in (b) of FIG. 2. On this account, if links or overlaps of islands occur in increased proportion in neutrophils by some reason, the accuracy of classification is impaired. The coincidence between the manual classification of neutrophils and the above-mentioned conventional automatic classification is 74%, and the accuracy of automatic classification technique is not yet satisfactory.